Baricitinib is a Janus Kinase (JAK) inhibitor. It is chemically designated as {1-(ethylsulfonyl)-3 -[4-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)-1H-pyrazol-1-yl]azetidin-3-yl}acetonitrile, having the structure as depicted in Formula I.

Processes for the preparation of baricitinib are disclosed in U.S. Pat. No. 8,158,616.
Polymorphism, the occurrence of different crystal forms, is a property of some molecules. When polymorphism occurs, the molecules arrange themselves in two or more different ways in the crystal, giving rise to differences in crystal structures and physical properties like melting point, thermal behaviors, X-ray Powder Diffraction (XRPD) pattern, Infrared (IR) absorption fingerprint, solid state NMR spectrum, and solubility. Thus, the discovery of new polymorphic forms of a molecule is important in the development of pharmaceuticals, as they may provide materials having desirable processing properties, such as ease of handling, ease of processing, storage stability, ease of purification, improved dissolution profile, and/or improved shelf-life.
There are no reported polymorphs of baricitinib.